A blister package is formed in a packaging method of forming a container by heating and shaping a plastic sheet to form one or more sunken spaces, putting an article to be stored in the container, covering the opening part of the container with a substrate such as paper, cardboard, a plastic film, an aluminum foil, and so on, and sealing the surrounding of the article. Such blister package is being applied to various fields of foods, batteries, toothbrushes, pharmaceuticals, stationery, and so on, because it can raise a demonstration effect by exposing the product through the shaped transparent parts, and it is possible to write specific information on the opposite substrate.
The plastic container and the substrate in the blister package are generally bonded by heat sealing. For this reason, the plastic container is made of a resin having a heat seal property. The substrate is also coated with the resin having a heat seal property. Therefore, the resins for a blister package basically require not only the heat seal property but also suitability of coating to be coated on the substrate.
Heretofore, a solvent-based resin solution has been used as the coating solution having a heat seal property. However, there is a fire risk due to the flammability of the solvent-based resin and a problem that an organic solvent may remain in the package. Particularly, since the blister package is mainly used for foods, pharmaceuticals, and stationery, and the organic solvent directly affects a human body when it remains in the package, the solvent-based resin is not preferable for the uses.
To make up for this disadvantage, the method of using a waterborne styrene-acrylate resin as a resin for a blister package was suggested. However, the resins for a blister package that have been suggested until now are poor in heat seal property in comparison to prior solvent-based resins at the same temperature condition, and there is still a problem that the plastic container is deformed when it is heated to the level of heat adhesion.